The present invention relates to a pusher head for feeder for automatic lathe, intended to equip a pusher and to intervene leaning against the rearward end of a bar of material to be machined, to push this bar in the direction of the lathe, this head including, to fit against the bar, a front recess which presents at least one inside conical surface part.
In practically all automatic feeders for machine tools, typically for automatic lathes, there are bar-guiding tubes which contain a pusher provided at the front, i.e., in the direction of the lathe, with a pusher head which pushes the bar of material to be machined toward the lathe. The pusher head is rotary, as well as, in general, the body of the pusher situated behind its head. At the rear of the body of the pusher, the latter is joined to a piston or other device for the application of pressure, this latter being most often non-rotatable, its connection to the pusher being made by means permitting mutual rotation. An illustration of such a conventional pusher is to be found, for example, in the Swiss patent specification No. 514,381. An identical design is used in the "Hydrobar"- type feed apparatus, manufactured by the firm LNS in Orvin, and the leaflets and maintenance manuals of which are at the disposal of the public.
In general, the rearward end of the bar of material to be machined was prepared by machining giving it a cone shape or else creating a frustoconical surface at the edge of the rear face of the bar. This latter way of proceeding is, for example, illustrated in Chapter 3.4.1.1. on page 14 of the instruction manual (accessible to anyone) for the "Superhydrobar" feeder, manufactured by the firm LNS in Orvin (CH). This same necessity of preparing the rearward end of the bar frustoconically is illustrated in FIG. 2 of the present specification.
The reason why it was hitherto necessary to prepare, conically or frustoconically, the rear of the bar of material to be machined coming to lean against the pusher head is explained by a glance at FIG. 1 of the present specification. One finds that if the rearward end of the bar were not suitably prepared, the widely open cone-shaped recess one had in the conventional pusher heads was liable to position the rear of the bar of material in a non-centered manner relative to the axis of the pusher. This appears obviously if one considers the rear face of a bar of material to be machined, in the rough state, assuming, something which may easily happen at the time of sawing the bar lengths, that the rearward end face is not absolutely perpendicular to the axial direction. FIG. 1 shows that that leads to an eccentric shifting e.sub.1 of the bar. Moreover, at the time of the preparatory sawing of the bar, it may frequently happen that the edge of the sawed face presents a burr of some kind, and, again, even if the rear face is perpendicular to the axis, this burr brings about an axial shifting e.sub.2 of the bar if the latter is placed in its rough state against the pusher head. This is the reason why, until now, the rearward end of the bar of material to be machined was always prepared to create there a conical or frustoconical centered surface, as shown, for example, by the accompanying FIG 2.
This additional operation of preliminary preparation of the rear bar end before it is placed in a feeder bar-guiding tube increased the cost of the operations of feeding bars to an automatic machine tool, typically an automatic lathe.
It would be well to mention here two prior publications which, in a certain way, touch on the problem of the centering of a part or bar in a rotary tip presenting a recess which comprises at least parts of conical surface. It is a matter of the specifications U.S. Pat. No. 2,118,301 and GB-Pat. No. 2,059,308. To tell the truth, the rotary tips proposed by these specifications are not feeder pusher heads but really spindle or counter-spindle fittings of lathes.
The American specification proposes a rotary tip which includes a widely open conical recess (30.degree. on the longitudinal axis). In connection with its FIGS. 5 and 6, this prior specification proposes providing the conical interior of the recess with ribs to prevent possible burrs of the part or bar end engaged from spoiling the centering of this part or bar. The burrs are supposed to enter the space between two ribs. If, however, a burr turns up directly at a rib, the non-spoiling of the centering first involves a rotation of the tip relative to the bar, failing which the burr spoils the centering nevertheless.
The British specification proposes a rotary tip presenting a frustoconical recess, free of any ribs, the angle of conicity of which is 8.degree.30'. One notices that the rotary tip according to this British prior publication is intended to hold the end of a wooden bar in engagement on a wood-turning lathe. The gripping of a wooden bar end in the inside cone, of low conicity, of a metal tip necessarily involves a certain compression of the wood. The end of a bar of metal would react differently. In this British specification, the advantage of the conicity chosen is presented as residing in a gradual increase in the force. Nothing is said about an effect of improving the centering obtained by a relatively low conicity.
An object of the present invention is especially to provide a pusher head for feeder for automatic lathe which permits the use of a bar in its rough state, i.e., the rearward end of which need not have been previously prepared to obtain sufficient centering of the bar of material to be machined relative to the pusher head.
In accordance with the invention, this object is attained by the presence of the features recited in the accompanying claim 1.
Advantageously, the mentioned ribs are six in number, and the angle of conicity of the frustoconical sector-based surfaces is from 2.degree. to 5.degree. relative to the axial direction.
The very low conicity of the frustoconical surface portions which receive the rear bar end means that even a relatively oblique cutting-off of this rearward end, though it theoretically brings about a very slight decentering of the bar, keeps this decentering at so insignificant a level that it can, without any doubt, be disregarded in practice. Moreover, the presence of possible burrs will not be disturbing, for at the moment when putting in place occurs, the burr will be lodged in the interstices between the ribs, where it will not disturb the centering of the bar, or else if the burr comes onto a rib, the latter will force it back toward the rear. In addition, the longitudinal edges of the ribs will be able, if necessary, to act as cutting edges to promote the forcing back of the burrs. The combination of the presence of the ribs and of the reduced conicity makes the arrangement according to the invention capable of forcing back suitably, and if necessary, of shearing off, rear bar face burrs or messy edges, until the bar is completely fitted in the pusher head with sufficient centering precision.
The invention attains the performance of remedying the risks of centering faults, which performance was not attained (not even suggested, made obvious) by the prior art.